Reply to "No Back up lights"

Wow Marlin !, Thanks for your research and detailed wiring analysis. I am not sure if this answers your question, but please bare with the electrically/mechanically challenged. I used my test light on the switch at the outside terminal and after removing the cover and cleaning up the inside contacts. I did have power on both inside contacts with the plunger depressed. Are you asking me to try the contact with the white wire outside terminal ?

I will also confirm my center ground. I was under the impression that all rear lights grounded at the two studs on the housing.

Last I will reinstall one of my old light assemblies and see if I had back up lights. I have been told that some assemblies had different contact pin placement such as Euros with the lower amber lens.

Thanks again, to all for your suggestions.
Jeff